Inductive measurements and study of the upper critical field in UBe13 single crystals as a function of field orientation

Using sensitive mutual induction techniques, we have measured the real part of the susceptibility, χ'(B,T), and the imaginary part, χ''(B,T), for three UBe13 single crystals below 1 K and in fields up to 8 T oriented along the [100] and [110] directions, with particular emphasis on the region near the zero-field critical temperature Tc. In this regime and within our experimental uncertainties of 0.5 mK and 5 mT, no anisotropy was observable for any of the samples. For all three samples, the magnetic susceptibility between 4 and 15 K was measured and subtle features were found for two of the samples around 10 K. For one of these specimens, an anomaly in χ'(B,T) was observed below the superconducting transition and is likely due to flux pinning mechanisms. The Bc2(T) phase diagrams are presented and compared to the results of other workers. Finally, the temperature dependence of the penetration depth for 0.1≤T/Tc≤0.5 was found to be close to T3, independent of field orientation, and these data are presented and discussed